Delete child record (from entire database) from parent form without deleting parent record

Delete child record (from entire database) from parent form without deleting parent record

Parent Form: Incident
Child Form: Task 

If I delete a Task from the "All Tasks" report, it is removed from the Incident Form. 
I used deluge scripting to delete the Task record when I delete the Incident record. 

If I delete a Task record from the Incident record (but I do not delete the incident itself), the Task remains in the "All Tasks" report. I need the Task to be completely deleted from the database if it is deleted from the Incident. 

Ideas?