Just a note to those who find this thread while searching for a way to stop LastPass suggesting all of your passwords for a whole domain...
You don't have to add every subdomain as some users seem to be suggesting, you only need to add the parent domain. So, for example, if you had several servers all under one domain:
You would only need to add "domain.com" to URL Rules under Account Settings with the "Host Matching" switched to Yes, and then all subdomains get their own unique set of passwords. (Don't forget to go to Account Options > Advanced > Refresh Sites in your browser plugin to pick up your changes)