From the document cited by Mike Jones:
Originally Posted by CT OLR
Additionally, a person is not justified in using deadly physical force if he knows he can avoid doing so with complete safety by:
1. retreating, except from his home or office in cases where he was not the initial aggressor or except in cases where he a peace officer, special policeman, or a private individual assisting a peace officer or special policeman at the officer's directions regarding an arrest or preventing an escape;
The law does not say you can't check your own home for possible intruders.
However, I think the OP (or the instructor) is unclear on terminology. A "home invasion" is where the invaders basically break in the door and go right for the occupants. A home invasion is quite different from a burglary, where the intruder tries to sneak in and would prefer to grab some loot and escape without having a confrontation with the occupant(s).
IMHO, if it's a home invasion, you won't need to "sweep" the house to find the intruders, because they will already have found you. It's the "hot" burglaries (burglaries while the premises are occupied) that are likely to make things go "bump" in the night and possibly lead to "sweeping" the house to check for intruders.
Looks like sweeping is not prohibited, but I'm sure a lot of personal protection trainers will tell you it's a dumb thing to do.
BTW -- who was the "expert" who said this? Was this the firearms course instructor, or an attorney? I ask because I'm an NRA certified instructor. I'm pretty sure the course Connecticut looks for is the NRA 'Basic Pistol" course, which is one of the courses I'm certified to teach. And the NRA is VERY clear that in presenting this course (or any course) I am NOT allowed to offer any advice regarding the law. I am supposed to find a qualified attorney or LEO (yeah, right, an LEO who knows the law -- guffaw) to present that segment of the class.