http://blog.chron.com/ultimaterockets/2014/05/rockets-fire-assistant-coach-dean-cooper/#23049101=0 He was hand picked by McHale. Even McHale will be back (still not 100% sure at the moment), it seems his hand picked assistants will be gone mostly.
Probably just the first of a couple different changes to be made to the assistant coaching staff. Not that Cooper did anything bad, its just that they probably need room for some new guys coming in.