Are you able to tell if there are any injuries?
Do you know whether any blood was on the reds too? (Of course, it would be less obvious on red chickens than on white ones.)
I suggest you look especially at the combs, because comb injuries can bleed a LOT. If one or more birds have injuries to their combs, and if you find no other injuries, then it's probably fine to just watch for a few days--it might be a one-time thing. (And paying extra attention means that any repeats will be noticed. You might have to fix something sharp, or separate bullies/victims.)
I once found blood splattered all around the (formerly white) walls of a large chicken coop, all the chickens acting fine: and one small scab on the comb of one rooster. I never found any other injury from that incident, did not change anything, and it never happened again.