I'm sure someone like JPC or the like will be along to give the ultimate info, but before doing anything you'll need to see how deep it goes - is it too deep to polish out?
If you are able to polish it out, then you'll need to make sure the scratch is completely clean of any grit or contaminents.... i guess clay would do the job once cleaned over to ensure nothing is caught in it that would then harm the surrounding paintwork.
Then depending on how big it is, i guess something like ScratchX might do the job. Depends how long, deep and visable it is really.