Well, taking a cue from other sports, one way would be to give either team the chance to challenge the decision the next time the ball goes dead (perhaps allow one or two challenges per team per half).
In the rare scenario where the next time the ball goes dead is when the other team scores, and it turns out the original 'clearance' should have been a goal, then the first goal is given and tough luck on the other team. (But if the correct decision had been given in the first place, they wouldn't have been able to run straight up the park and score anyway. One time in a thousand they might just have done it straight from the subsequent kick off, but this way they still get their opportunity to do that.)
If it turns out the original 'clearance' really wasn't a goal anyway, then the team that ran up the park and scored gets to keep their goal, and everything's hunky dory.