KevinKyburz clearing the cache works and inkognito mode to
So that means there is no server problem, you fixed it :-)
Their web browser is caching/remembering the previous problem (so sending their domain to the first domain on the server)
Just to be clear - web browser caching is completely different to server caching :-)
Their cached version will expire and just start working in time, but if they want to see it now then clearing the cache or viewing in incognito is the only way to see the live version. There's nothing you can do on the server to make their web browser behave differently.