Don't mark channels as unread when all unread messages have been deleted

As a server owner, it is incredibly grating that if a spam bot starts sending messages with links to all of my channels and those spam messages are deleted by banning that spammer, these channels will still appear as unread to all of my users.

 How are the members of my server supposed to know which channels actually have new messages if clicking on a channel with the unread icon shows a channel with no new messages? 

So please, at least give us the option to make it so that the unread mark is removed in these cases.

 Otherwise, raids and spambots will continue making servers less usable even after all of their messages have been deleted.

A related issue and another possible solution is this one: Unread message count on every channel