You should list the version of Oracle that you are using and the operating system for your database server. Generally I don't use the domain. I'm not sure why someone would want to except for people who also SQLNET.AUTHENTICATION_SERVICES= (NTS) whcih I don't use either.

You can comment out the SQLNET.AUTHENTICATION_SERVICES= (NTS) as well as NAMES.DEFAULT_DOMAIN = XYZ.COM and you should be able to access your database. If not post the above items and someone might have an answer.