According to the toolkit help system, Get-NcCifsPreferredDomainController must be directed to a specific SVM whereas Get-NcCifsDomainServer can be directed to either the cluster connection or an SVM.
You can determine this behaviour by looking at the Family attribute in the output of `Get-NcCommand <cmdlet-name>` (example below).
* Family 'vserver' means the cmdlet must be directed to the SVM (either create a connection to the SVM directly or specify the Vserver parameter when connecting to the cluster or provide a value for the VserverContext parameter when running cmdlets of this family).
* Family 'cluster' means the cmdlet must be directed to the cluster (i.e. will fail if you are directly connected to an SVM).
* Family of 'cluster, vserver' means you can direct the cmdlet to either an SVM or a cluster.
PS C:\Users\aparajir\Perforce\aparajir_BTC_pstk_3\main> Get-NcCommand Get-NcCifsPreferredDomainController
Name Category Family Api
---- -------- ------ ---
Get-NcCifsPreferredDomainController cifs {vserver} {cifs-domain-preferred-dc-get-iter}
PS C:\Users\aparajir\Perforce\aparajir_BTC_pstk_3\main> Get-NcCommand Get-NcCifsDomainServer
Name Category Family Api
---- -------- ------ ---
Get-NcCifsDomainServer cifs {cluster, vserver} {cifs-domain-discovered-servers-get-iter}
Hope this helps!