Usually it will heal by itself.
Do you know if it was caused by the other chin? If so, I would separate them. Once one draws blood from another, it can get worse the next time.
Could it have been caused from something in or on the cage? Sometimes the clips that hold a cage together have sharp edges and are not properly closed. Sometimes all the cut edges of the cage have not been properly smoothed. I would check the cage carefully for these. If you have a "J" feeder, check where the wire fits into the feeder (where your little one would be sticking it's little nose to reach more pellets. Another place is where the ramps are attached or around the door.
Most bad open sores should be flushed out with saline/iodine solution (looks like the color of weak tea), but the wound being around the nose, I would not try to flush it out.
http://www.geocities.com/jobernstein1949/ Read the article Nursing & Damage Control. CAUTION: This article is not for children or the squeamish!
Like Jamie said, keep an eye on it for any fever or redness. If that happens, get it to a vet a.s.a.p.
If it is just a small scratch, you probably will not have to worry about the scratch itself, but you may want to be a little concerned about leaving the two chins together.
Jo Ann