There is an unloadAll method on the DS.Store, but you have to call it per type. So for example, in a controller or route, you could call this.store.unloadAll('phoneNumber'); to unload all PhoneNumber models.
I opened a question recently about some errors I was getting. Turns out you can’t call unloadAll during a loading state, so not from the beforeModel, model, afterModel, activate, or setupController methods of a route. I haven’t confirmed all these, but my errors turned up in the logout route’s activate hook. I think the better place to do the unload stuff is in an action handler.