The Domain element contains the FQDN (2) of the domain containing the domain controller.

 <xs:element name="Domain" nillable="true" type="xs:string" />

The Domain element is populated from the nTDSDSA!msDS-hasDomainNCs attribute on the nTDSDSA object specified by the GetADDomainControllerRequest/NtdsSettingsDN (section input parameter element , converted from a DN to a canonical name following the syntactic transformation described in [MS-ADTS] section, but with any trailing "/" omitted. If the nTDSDSA!msDS-hasDomainNCs attribute is not present or cannot be read due to the client lacking access rights to read the attribute, the server returns a null ActiveDirectoryDomainController/Domain element.