qweoig yes, contact storage is the app you're looking for. Clearing storage of that will delete all contacts on device. Be sure to disable DAVx5 sync before doing that though, since I'm not sure if the changes would get synced back to the server.
Followup question: so you're saying the DAV contacts are showing in the contacts app only? All apps are on the same profile, correct?
If you create a new contact from the contacts app with the server as the destination, does it sync over the changes?