We're using Trello to track our hiring process. It would be nice to use the "vote" feature to quickly gauge opinions without having to read comments. However, there doesn't seem to be a way to clear votes besides having each member unvote. So, votes currently must represent the card over the whole board. It seems reasonable for it to represent the card only for that list, but that's only possible if you can clear it somehow...
You can always remove your own vote, but not other member's votes.
You can disable votes via the preferences page (click the 'preferences' button on the sidebar) or limit the permissions on who can vote (board members, organization, public).
No, I don't believe there is, having just tried it out. Nor can I see any mention of it on the Trello development board.
Depending on how many cards you have, and with how much info, a workaround might be to just replace existing cards with new ones of the same name (and no votes).
You could send your suggestion to firstname.lastname@example.org, as suggested in the Trello Help.