Disclaimer, I haven't looked at GRC explicitly, but often tools like this will * check whether a range of domains are censored by the DNS * lookup a bunch of

Disclaimer, I haven't looked at GRC explicitly, but often tools like this will * check whether a range of domains are censored by the DNS * lookup a bunch of domains and ping them to check whether the DNS server is returning properly localized addresses using EDNS - Cloudflare DNS is a good example of one that was not (at least a few months ago)