Soap doesn't actually do any killing, unless it is spiked with antibiotics (which we are learning was a bad idea), it just surrounds debris to be rinsed off.
My suggestion would be to stick with the regular brewery cleaning scheme...ie. PBW or oxyclean, rinse, sanitize. However, if this is a plastic carboy, your chances of contaminating your next brew are a bit higher. You might consider labeling this carboy as your sour-carboy from here on out, as many people do.