Quirky Domain Mapping Action - Plugin Redirects Back To Source

I had a domain point to the IP where my WPMU site is hosted. I set the domain mapping of the sub-domain on the WPMU blog with the name of the domain it should appear to be.

When I type in the subdomain name, it resolves to where the mapped domain previously pointed. When I type in the name of the mapped domain, it resolves to its former location rather than the subdomain that has tried to take advantage of the domain mapping plugin.

(1) Is this a delay in the migration of the DNS records across the interweb? (It has been six to eight hours), or

(2) Is there some setting I failed to make?

Thanks,
Kirk