Translation:Clean your mind!
I understand the sentiment but the more common idiom would be" "Get your mind out of the gutter"
Clear your mind would be better? It's not related to sexual thoughts at all. Basically clearing your mind of busy thoughts, stress. Switch off.
Probably something to do with jumping to conclusions of a sexual nature without being given enough evidence. You could say this admonishingly to somebody who accuses you of taking a sexual interest in a piece of art when you admire it for artistic purposes.
In British English you can accuse someone of having a "dirty mind", so the sentiment of this sentence is, that rather than let that stand, to actively apply some "brain bleach".
I like that. I will keep that in mind next time I have dirty thoughts hahaha
Another common english phrase that has a similar meaning would be 'Get your mind out of the gutter!' Hope this helps.