Gets AD group members from multiple domains and can also do recursive lookup. Uses string manipulation to get Domain and if fails uses GC

Get-GroupMembers.ps1

function Get-GroupMembers
{
	param (
		[Parameter(
				   Position = 0,
				   ValueFromPipeline = $true,
				   ValueFromPipelineByPropertyName = $true,
				   ValueFromRemainingArguments = $false
				   )]
		[ValidateNotNullOrEmpty()]
		[Alias('Name', 'ADGroup')]
		[string[]]$GroupName,
		[Parameter()]
		[Alias('Recursive', 'Indirect')]
		[switch]$Nested
	)
	
	
	foreach ($Group in $GroupName)
	{
		
		#Getting Domain Value for global catalog try if required
		$Domain = Get-ADDomain | Select-Object -ExpandProperty Netbios
		
		[array]$AllMembers = Get-ADGroup -Identity $Group -Properties * -Server "$Domain`:3268" | Select-Object -ExpandProperty Members
		
		$a = 0
		
		foreach ($member in $AllMembers)
		{
			Write-Progress -PercentComplete ($a / $AllMembers.count * 100 ) -Activity "Enumerating Group: $Group" -CurrentOperation $member
			$a++
			
			$Split = $member -split ",DC="
			$Join = $Split[1 .. ($split.count)] -join "." -replace """", ""
			
			$DN = $member -replace """", ""
			
			#For some reason get-adobject sometimes errors. If thats the case try using global catalog
			try
			{
				$obj = Get-ADObject $DN -Property * -Server $Join -ErrorAction Stop
			}
			catch
			{
				#Try using Get-ADUser and Get-ADGroup instead in a nested Try statement
				try { $obj = Get-ADUser $DN -Properties * -Server "$Domain`:3268" -ErrorAction Stop }
				Catch{ $obj = Get-ADGroup $DN -Properties * -Server "$Domain`:3268" -ErrorAction Stop }
			}
			
			if ($Nested)
			{
				if ($obj.ObjectClass -eq "group") { Get-GroupMembers -Group $obj.DistinguishedName }
			}
			
			[System.Array] $Objs += $obj
		}
	}
	
	Write-Progress -Completed -Activity "Completed Enumeration"
	
	$Objs
}