iOS Reset nav controller to top view when switching within UITabBarController

Hi everyone,

I'm probably missing something really basic here... but how do you reset a navigation controller to the top view controller when switching between views in a UITabBarController?

i.e. I have 4 tabs in my app, each of which has their own navigation controller. Some of the tabs drill down multiple levels. I would like to set it so that, for example, I can go into tab 1 and drill down to level 3, switch to tab 2, switch back to tab 1 and NOT be still in the level 3 view, but back to the top view.

Thanks in advance!