I recommend you just ignore it. But to clean it one method is to remove the nozzle and soak it in acetone for an hour and anything that doesn't wipe off after that I would burn off with a flame.
But taking the nozzle out of the head is tricky and you can break the temp probe cable if you aren't careful. Sometimes the probe slides out easy (after removing the very skinny screw) but other times it's just stuck the hell in there and almost impossible to remove without drilling it out and destroying it.
Unscrew the four screws that holds the fan bracket to the head so you get full access to the nozzle (you can just let the fanbracket+fans dangle while you work. Try to keep it out of the rear fan and away from the heat though). Heat the nozzle up to about 100C, pick away the bits you can get off. Heat up to printing temp and get any stubborn bits. Acetone is pretty decent at dissolving ABS so that can also help (just remember that it's highly flammable).
Some heat and patience should get rid of it.
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