Sven Co-op Entity Guide

Advanced trigger filtering
  Generic information

Advanced trigger filtering was introduced in Sven Co-op 4.5. It allows entities to enforce requirements on their targets' and caller's targetnames and/or classes in order to receive triggering. Trigger filtering only operates on the direct triggering system. For example, you cannot use this to exclude a player with a specific targetname from triggering a trigger_multiple by walking into it; you'd need to use a trigger_condition entity for that instead.

Trigger filtering-keyvalues:
The following keyvalues can be set on entities to enable trigger filtering. Note that although this works for all entities, not all entities have these keyvalues; this was done to prevent bloat. You have to disable Valve Hammer Editor's smart edit-mode to add them manually then.
Indeed, targetname out-filtering is trivial, since you know by what name you're targeting.