Is there a way to make vertexes "forget" other bone weights?

I’m trying to rig a model, and am hitting a really annoying snag. I now have several vertexes who are %100 weighted to more than one bone. So they try to maintain a compromise between all their movements.

Simply put, lets say you make a head bone and then the model’s head. And then assign all the vertexes to the head bone. Then you make a jaw bone and assign the jaw vertexes to the jaw bone. But now your jaw is horribly deformed when it moves because it is trying to follow the jaw and head bone at the same time.

Is there some way I can just select the jaw bone and say it has exclusive rights to those vertexes? I would really rather not go in and manually unweight all of the vertexes from any other bones.