You can "leave" the domain on the offending system (using adleave with the --delete option) but depending on the environment it may be a no-no because you may compromise the availability of a production system.
If your environment is doing the right thing (enforcing separation of duties) it's time to walk over to the Windows or Active Directory side of the house and ask for help.
The "setspn -L [system-name]" command in Windows allows you to query Active Directory for the offending system.
Also if you rename your system correctly (depending on the distro, this may not be very trivial) or use the "-n" option you can get around this.
R.P