Device Groups contains old entries

Device Groups contains old entries

Good afternoon,
 
We have device groups in our installation for different areas of IT so they view only what they need.   When I go into Device Groups and modify a group, the list of Available Routers still shows routers that are no longer in our environment.  Is there a way to refresh this information?
 
If it helps, we are running Professional 9.1 Build 9100.
 
thanks.

                New to ADSelfService Plus?