Multiple domain search

How is it possible to search on multiple domains in Get-ADUser Query?
I have 3 domains -,,

		Get-ADUser -Identity $_.samaccountname -Properties *

Are the domains in the same Forrest ? If so you could probably do something like this :-

$Domains = (Get-ADForest).domains

ForEach ($Domain in $Domains) {

$UserAccount= Get-ADUser -server $domain |
select SamAccountName

$Users += $UserAccount

$Users| Export-CSV Users.csv -notypeinformation

Unfortunately they aren’t in the same forest.

Map a PSDrive to each domain using the AD provider. Change to each drive in turn and run your query.