I have a sub-domain network installation on http://www.example.com
One of the sites is rabbit.example.com
This site used to have a domain mapping to http://www.rabbit.com.
I removed this mapping.
I have checked the site settings for rabbit.example.com, and the base URL and home URL are set to rabbit.example.com.
I have double-checked the domain mapping is no longer there.
I do not have a caching plugin installed.
The site's database table, wp_10_options, has the site URL as rabbit.example.com