Sort Posts by Last Comment / Activity

I can’t find a way to sort posts by their last activity.

The idea is to have posts listed like normal when they have no comments, but when a post receives a new comment, bring it back to the top of the post list. That way my post list will contain the most recently talked about blog posts. I would like it to function much like most forums do.. such as this one. The “freshest” content stays on top.

Any way to edit the loop query to make this happen?