Unless you're a blockchain analysis expert it is hard or even impossible to determine if yours coins are clean or not. Bitcoin is so mixed that there is no absolutely clean coins (maybe those fresh mined).
Besides, the definition of "clean coin" sometimes is vague, few thought about privacy while others thought about whether the coin comes from illegal/questionable action.
IMO even freshly mined coins & pools might be monitored which could deanonymize miner who use public pool.