How do I get rid of Adobe flash update virus on Safari browser?

Hello. I've been having problems with a pop-up asking me to update my adobe flash player in my Safari browser. It blocks everything - and if I close it - it closes the entire site I was trying to reach. I know it's a virus/scam/malware because when I go to the adobe site, it says my flash is up to date.

This only occurs with the Safari browser - not with Chrome or firefox. I've tried using malwarebytes and Avast - and neither find the malware.

I've tried clearing my caches and that doesn't work either.

Does anyone have a solution?