Do you not have a GL account or something where you store funds/escrow for cashier's checks that never cleared? You would follow the state escheatment rules on this, but you wouldn't have to hold the physical check necessarily. I'd still try to find them to save you the hassle of sitting on it for the next few years, but you can only do so much before you just put it away until it's time to forward to the state.
Late response, I know!
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Someone's about to get horned!