Varnish cache not region aware
Possible solution of separating your caches, by regions, in Varnish is to use GeoIP VMOD: https://github.com/lampeh/libvmod-geoip

Simple example:

put country code to hash

sub vcl_hash {
        hash_data(req.url);

        if (req.http.host) {
                hash_data(req.http.host);
        }
        else {
                hash_data(server.ip);
        }

        # separate caches by countries
        hash_data(geoip.client_country_code());

        return (hash);
}


Now caches for different countries will be different. 
Of course, you still need to take care about page generation in Drupal, it should provide different content for different regions too.