Whats the "official" way to not be a MA resident anymore?

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So i moved across the border from MA to RI a couple months ago, so i'm figuring i'm a RI resident and not a MA resident anymore. Well, i get my 2007 estimated tax vouchers from MA the other day, i always paid my MA taxes this way when i lived in MA and worked in RI. So by getting this, i'm assuming i'm somehow still a MA resident! is thier an official form or something i need to fill out to no longer be a MA resident? I dont need to be paying taxes to a state i dont live in anymore!