Like literally filling the cavity. The point being, if the frame is full and occupied, there isn't any room for fouling/dirt to gather. Instead, what little can get in there will be held in suspension. The grease tends to migrate as the action is cycled.
An additional feature that keeps most of the fouling out of the action is an action shield. It's a cover for the action that mounts on the hammer. Every S.A. exposes the action every time it's cycled. Dirt has a direct pathway in. With a cap gun, you also have blowback through the nipple with each round. It follows the curve of the hammer right into the action. The shield blocks the fouling and also any spent caps/fragments and those are presented each time the hammer is drawn back. All the shooter has to do is turn the revolver upside down and the debris will fall out.
With the shield in place, casual shooters don't have to worry about disassembly for cleaning. I tell my competition shooters to check it once a year. If they see mostly red, close it back up and check it again next year. Cleaning chores are barrel, cylinder wipe down the frame and swab the hammer channel with a Q-tip and ballistol. That's about as easy as it gets.
Mike