#requires -Module SqlPS 
#requires -Version 5

Import-Module SqlPS -DisableNameChecking

function Get-CMSServers{
    param(
        [string[]]$CMSGroup = @('Group1', 'Group2')  #default groups...
    )

    function Get-RegisteredServers{  
        param(
            $ServerGroup,
            $ParentGroup
        )

        $ServerGroup.RegisteredServers | %{
            $objects.Add([PSCustomObject]@{
                ServerName = $_.ServerName
                GroupName = $ParentGroup 
                GroupDescription = $_.Description 
                ParentName = $ServerGroup.Name
            }) | Out-Null
        }

        if($ServerGroup.ServerGroups.Count -gt 0){
            $ServerGroup.ServerGroups | %{
                Get-RegisteredServers -ServerGroup $_ -ParentGroup $ParentGroup
            }
        }
    }

    $objects = New-Object System.Collections.ArrayList
    Set-Variable -Name objects -Option AllScope

    try{

        $srvConn = New-Object Microsoft.SqlServer.Management.Common.ServerConnection "ServerName"
        $ServerStore = New-Object Microsoft.SqlServer.Management.RegisteredServers.RegisteredServersStore $srvConn
        $ServerStore.DatabaseEngineServerGroup.ServerGroups | where{$_.Name -in $CMSGroup} | %{
            Get-RegisteredServers -ServerGroup $_ -ParentGroup $_.Name 
        }

        return $objects;
    }
    catch{
        $_ | fl -Force
    }
    finally{
        $srvConn.Disconnect();
    }

}

Get-CMSServers -CMSGroup @('Production', 'Reporting')