script.ps1

foreach ($vdi in $vdis) 
{ 
    $n = $vdi.name
    $AdComputer = Get-ADComputer -identity $n -ErrorAction SilentlyContinue
    $Citrix = Get-BrokerMachine -HostedMachineName $n #-ErrorAction SilentlyContinue
    $VmWare = Get-ProvVM -VMName $n #-ErrorAction SilentlyContinue
    if($AdComputer)
    {
        #Exists in AD, do action here, read from console what ever
    }
    if($Citrix)
    {
        #Exists in Citrix, do action here, read from console what ever
    }
    if($VmWare)
    {
        #Exists in VmWare, do action here, read from console what ever
    }
    #Or all together
    if($AdComputer -or $Citrix -or $VmWare)
    {
        #One the objects are not null, do action
    }
}