Android : How do I dismiss a dialog fragment shown by another activity from a different activity?

What I want to do

I have a dialog fragment shown from Activity A which contains a button. When the button is pressed Activity B is started. Within activity B, what ever action the user does causes activity B to end via a call to finish() however I wish to dismiss the Dialog fragment from Activity B before the call to finish() so that when the user navigates back to activity A, this dialog is no longer shown.

The problem

As you see in the code section, I have recreated the problem on a small scale to avoid posting huge amounts of code and to simplify the question. The issue is that the application I have contains a lot of activities which can show the dialog fragment so I do not know how to keep track of the activity which started the dialog fragment. However I know that another activity cannot find fragments added from another so I was wondering if there is someone who knows a way around this problem.

The code

Dialog Fragment

public class MyDialogFragment extends DialogFragment {

    public static final String TAG = "MyDialogFragment";

    public static MyDialogFragment newInstance(){
        MyDialogFragment myDialogFragment = new MyDialogFragment();
        return myDialogFragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View view = inflater.inflate(R.layout.mydialogfragment,container,false);
        Button goToSomeOtherActivity = (Button)view.findViewById(R.id.goToSomeOtherActivity);
        goToSomeOtherActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(getActivity(),SomeOtherActivity.class);
                startActivity(intent);
            }
        });

        return view;
    }

Activity A - which displays the dialog fragment on button press

public void showDialogFragment(View view)
{
    MyDialogFragment.newInstance().show(getSupportFragmentManager(),MyDialogFragment.TAG);
}

Activity B - This one attempts to close the dialog from activity A via a button click

    public void dismissDialogFragment(View view)
{
    MyDialogFragment myDialogFragment = (MyDialogFragment)  getSupportFragmentManager().findFragmentByTag(MyDialogFragment.TAG);
    if(myDialogFragment != null)
    {
       Log.d("SomeOtherActivity","Its not null, we got it");
    }
    else{
       Log.d("SomeOtherActivity","it was null :(");
    }
}

What I have tired

Below is what I have tried to do which did not work. I had the idea that if a global fragment manager was used to show the fragment and this manager should be able to find it.

What I did was create a base activity which Activity A and B extend from.

public class BaseActivity extends ActionBarActivity {

    private FragmentManager globalFragmentManager;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        globalFragmentManager = getSupportFragmentManager();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }

    @Override
    protected void onPause() {
        super.onPause();
    }

    public FragmentManager getGlobalFragmentManager(){
          return globalFragmentManager;
   }


}

Now activity A and B used this to show and attempt to dismiss the dialog fragment

In Activity A

   MyDialogFragment.newInstance().show(getGlobalFragmentManager(),MyDialogFragment.TAG);

In activity B

 public void dismissDialogFragment(View view){
        MyDialogFragment myDialogFragment = (MyDialogFragment)getGlobalFragmentManager().findFragmentByTag(MyDialogFragment.TAG);
        if(myDialogFragment != null)
        {
            Log.d("SomeOtherActivity","Its not null, we got it");
        }
        else{
            Log.d("SomeOtherActivity","it was null :(");
        }
    }

This still resulted in the dialog being null and not able to dismiss.