Cancel notification on remove application from multitask panel

I manage an ONGOING notification from my application (not from a service).

When I kill application from task manager with "End" button, notification disappear.

When I remove application from multitask pannel, application is killed but notification remains.

My questions are:

• How to catch this event to clear notification?
• What happens when application is removed from multitask pannel? Application is destroyed but process staying alive? Is it normal?

As an update:

All my activities extends MyActivity class (which extends Activity) with methods:

@Override protected void onCreate(Bundle state) {
    super.onCreate(state);
    ((MyApplication) getApplication()).onActivityCreate(this, state);
}

@Override protected void onDestroy() {
    super.onDestroy();
    ((MyApplication) getApplication()).onActivityDestroy(this);
}

And my application extends MyApplication class (which extends Application) with methods:

private List<Activity> activities = new ArrayList<Activity>();

protected final void onActivityCreate(Activity activity, Bundle state) {
    if(activities.isEmpty() && state == null) {
        onStart();
    }
    activities.add(activity);
}

protected final void onActivityDestroy(Activity activity) {
    activities.remove(activity);
    if(activities.isEmpty() && activity.isFinishing()) {
        onExit();
    }
}

protected void onStart() {
    // some code
}

protected void onExit() {
    // some code
    notificationManager.cancel(NOTIFICATION_ID);
}

activities is a list of all running activities

It's not simplest mechanism but I need it

Should I use a service instead?

As a new update:

In my onExit() method, if I Log debug message to know what happens like this:

public void onE