Efficient way to get rid of bookmarks

Is there a fast way to delete all your bookmarks that you synchronized with Xmarks?

this would come in handy for computers that aren't yours or that you're temporarily using, such as a school computer or a friends.

The best way I know of right now is to just go into the bookmark settings of whatever browser you're using and delete them manually, but if you have a lot of bookmarks, this can take a while.

Any ideas would be appreciated, thanks.