In my case, I only work within a particular OU in our Domain, so I’ve made it so my $Path can be abbreviated. Forked (https://gist.github.com/VertigoRay/6091753) ... here’s how I handle things:

gistfile1.ps1

[string] $RootOU = 'OU=test,DC=domain,DC=com'
[string] $Path = 'OU=foo'
try {
    $ou_exists = [adsi]::Exists("LDAP://$Path")
} catch {
    # If invalid format, error is thrown.
    Write-Debug "Supplied Path is invalid.`n$_"
    # It's probably the abbreviated version, so let's tack on the Root OU and confirm exists.
    Write-Debug 'Placing Path in Root OU and re-verifying ...'
    $Path = "$Path,$RootOU"
    try {
        $ou_exists = [adsi]::Exists("LDAP://$Path")
    } catch {
        Throw("Supplied Path is not valid, nor is our attempt to place it in the Root OU:`n$Path")
    }
}

if (-not $ou_exists) {
    Throw("Supplied Path does not exist:`n$Path")
} else {
    Write-Debug "Path Exists (1):  $Path"
}