If they throw in a frag, at this point are they worried about civilians? I would think not
It really depends upon the type of building and its occupancy. A multi-story structure is a lot more difficult than a one-story building, and the presence of noncombatants makes it ten times worse. Fragmentation grenades make a real mess when you've got civilians in the way. SOF types use concussion grenades in order to be a bit more selective, but there aren't enough SOF operators in the world to clear a city.
A key objective is to give your holed-up enemy the idea that he has a way out. Once he knows he's hopelessly trapped, he will fight like the demon and will be determined to take as many with him as possible. Clearing buildings is the single most difficult military task I can imagine...