That limits results to pages on example.com (or neg for the second) but that's not what OP is trying to do. Searches for "example.com" should return pages where

That limits results to pages on example.com (or neg for the second) but that's not what OP is trying to do. Searches for "example.com" should return pages where the exact domain "example.com" appears in the page. It does sort of work for "example.com" itself, because it's so common presumably, but doing it with other domains that are less common is far less likely to produce anything useful.