Given that Git is very SHA-1 friendly, I would surmise that it is possible to easily check for this scenario:
-I have a repo with a directory foo/ somewhere within it. -Someone on some other computer makes a change to foo's contents (including nested subdirectories), and pushes the change to the repo.
My guess is that I will have to do a fetch and check if there is some difference between the SHA-1 for my directory and the SHA-1 of the remote directory, but I don't know how to do this.