A strip cannot be synchronized, since it is the absence of a changeset. The original commit has been made public already, and it exists everywhere it has been pulled. Even if you remove it from the main repo, it may get pushed back again by another, eventually. If you want to remove it from the other repositories, you will have to strip it manually everywhere.
While this may be possible if the repo is private and if you control who has access to it, it can be harder for public repos. The best alternative is to leave the changeset while rendering it inactive.
To do so, simply merge the two heads of extratemp
on your local repo, by following these instructions to the letter. Then, your branch should only have one head, with your current state.