Get an account on that portal and submit the site for recategorization. Register here https://www.trustedsource.org/en/home/register?p=mcafee
I find myself doing this relatively frequently.
I have a rule where I can slap business critical sites that temporarily run afoul of McAfee categorization into a whitelist, and then set a reminder to circle back and remove those entires once mcafee finishes the recategorization. They used to turn these around within a business day but lately the turn around has been much slower for some reason. I have harassed The Appropriate Folks on this but haven't had one to submit lately.
What Regis suggested is correct (submit the site).
The issue at hand is coming about most likley because of the reverse lookup that takes place.
So while xyz.com may not be categorized, it's IP address used to host some pretty bad content, and the IP address of xyz.com is categorized as high/medium risk.