I had a lot of trouble finding how to do this and finally figured it:
- Login to ovirt admin console
- Go to Storage>Domains
- In the Domain Name column click on the name of your domain
- Click Data Center tab then click the maintenance button
- Takes a minute or so but once that is done click detach
- Go back to Storage>Domains and click Remove
References:
https://lists.ovirt.org/pipermail/users/2013-April/013858.html