I would recommend not worrying about it. Yes, you can block accounts, but you don't control who follows you, they choose to follow you. It says nothing about you if certain accounts follow you.
On a different note, don't you have better things to do than clean out your follower list?
I only report spammers if they actually say something to me @levyj413, and we never bother cleaning out followers on EPA's main Twitter account, @epagov.