This video (rather long, so best to fast forward) shows a group of climbers cleaning an old route in the Czech Republic. They use a log to lean against the rock, then a human pyramid to get a climber high enough to clean the rock and then to clip the one bolt. Here’s their website. Their rules for climbing are very strict – ground up, no bolting on rappel, no chalk. But apparently they can scrub the dickens out of the rock to remove lichen.