Injury First Aid for minor scratch?

I noticed that one of my pigs has a tiny scratch in the area just below her nose, but above her lip. It happened sometime after she sat on my lap today (maybe 1pm) but before I fed them their dinner veggies. She doesn't appear to be in any pain and I've been home all day, so I know there was no fighting; the two girls get along fantastically. I don't know how it happened (sharp hay, maybe?). I was just wondering if I'm supposed to do anything about it or just let it heal.