The Win32_ComputerSystem class represents a computer system operating in a Win32 environment. You can find more information here.

Win32_ComputerSystem has a PartOfDomain property that indicates whether the computer is part of domain or not. There is also a workgroup property – that should be blank if the computer is on a domain.

The Get-wmiObject cmdlet has its own alias as gwmi.

if ((gwmi win32_computersystem).partofdomain -eq $true) {
    write-host -fore green "The server/computer in Domain!"
} else {
    write-host -fore red "The server/computer is not in domain."
}