Bingo! Recently I've been working on resolving a bug with a small group of coworkers. We created a repo in which we have been rewriting public branches all the time. You just send an e-mail. Everyone just has to know how to migrate their local changes.

   $ git fetch # the rewritten world
   $ git checkout
   Your branch and 'origin/foobar' have diverged,
   and have 13 and 17 different commits each, respectively.
   (use "git pull" to merge the remote branch into yours)

Now I happen to know that only 3 out of the 13 divergent commits on foobar are my local commits. I rebase my local foobar branch to the upstream one, migrating just those 3, and ditching the remaining ten:

   $ git rebase HEAD~3 origin/foobar

Easy.

This is all just test code people are trying in investigating the bug. Any permanent fixes arising are properly cleaned up, commented, and submitted via Gerrit to a whole other repo where they are cleanly cherry picked to a linear trunk which is never rewritten.