How can we Write Off or close out the available quantities on a PO that has been written off ?

Whenever we perform write off of a PO receipt the the dollar amount of PO is wriiten off from an accounting perspective but from operations perspective the quantities on PO still show as available. You can match these quantities to invoices in EBS even though the dollar amounts have been released. When you match such quantities system puts a debit in accrual account where there is no credit any longer to offset it. How can we close out the available quantities on a PO that has been written off ?