It's not the lens, it's the reflector that's scratched.
Canned air will remove 99% of the dust particles that get inside a flashlight.
I've seen a reflector for a Maxa Beam cleaned using foaming soap and water with an alcohol rinse once cleaned to displace any water droplets. Plastic reflectors and the vapor deposited coatings are very soft. Use the canned air in an upright position only. The only air compressor that would be safe for use would be one of the low pressure airbrush diaphragm compressor.
Compressed air from an automotive type compressor contains small traces of water and compressor oil. It's use will lead to further contamination.