Get-DomainFromFQDN return the domain portion of a Fully-Qualified Hostname. This is currently limited to 4 sub-domains but the array selection could easily be extended to use the length of the array if appropriate. Useful for automatic deployment scripts.

Get-DomainFromFQDN.ps1

Function Get-DomainFromFQDN {
    param($fqdn)  
    
    $vmdomain = ($fqdn.split("."))[1..4]
    $vmdomain = $vmdomain -join "."
    return $vmdomain
}

$fqdn   = "myhost.my.domain.local"
$domain = Get-DomainFromFQDN -fqdn $fqdn
$domain # "my.domain.local"