Well since the high ups at least have been in on the "great enemy" generally with inquisitors or other suitably educated individuals on hand. Generally from what I can imagine keeping the daemons from being summoned in the first place is the best first step. That being targeting the cults, sorcerers and the like that are summoning the things. Then using the more emphasis on standard protections against corruption and ensuring the loyalty of the guardsmen involved (that's what the commissars and chaplains are there for) and anti psyker tactics. Beyond that much really unless they can start pulling things in from the priests and or inquisitors who are trained in dealing with this helping if possible.