Your best option is probably to listen for when the list dispatches Event.SCROLL. In the listener, you can probably do something like this:
var point:Point = new Point(0, 0);
if((point.y + itemRenderer.height) <= 0 || point.y >= list.height)
//out of bounds
Inside the item renderer, if you need a reference to the List, you can use the owner property.
Don't forget to remove the listener at some point, or you'll have a memory leak.