Untested: This will sync AD on all Domain Controllers

ADSync.ps1

Function Sync-AD {
    Param(
        [Credential]
        $Credential=$(Get-Credential)
    )
    $splatme = @{
        ComputerName = Get-ADDomainController -Filter {Name -like "*"}
        ScriptBlock = {
            Import-Module -Name 'ADSync'
            Start-ADSyncSyncCycle -PolicyType Delta
        }
        Credential = $Credential
    }

    Invoke-Command @splatme
}

Sync-AD -Credential $([System.Net.CredentialCache]::DefaultNetworkCredentials)