ActionScript 3.0 :: Garbage Collector - How To Dispose Off Unneeded Objects

I'm forgetting now exactly how I should dispose of unneeded objects. In the past, every object/class I created had a public dispose() function which removes all added listeners inside it and called the kill/dispose function on any children of it that may need the same (so it worked its way down the tree, as this process can continue for as many children/grandchildren there are in the list). So basically, the code in the parent class would look like this:

Code:
childObj.removeEventListener(MouseEvent.MOUSE_DOWN, anotherHandler);
childObj.dispose();
childObj = null;
...and the childObj class would look like this:
[Code] .....

Do I need to set any variables/objects defined in the child class's class scope to null prior to setting the class itself to null? Or is this handled automatically when I set the class itself to null from the parent (assuming these class-scope-defined variables/objects have no listeners or child objects which need to be disposed themselves)?