If you are using TaxCloud to report Sales Tax, you MUST Invoice the Customer to reverse the unreported revenue and tax that the Credit Memo sent to TaxCloud. 

DO NOT MANUALLY JOURNAL the reversal if you are using TaxCloud.  Make a new Customer Invoice.

This works for v13 and v14:

Create a Manual Journal Entry, making sure to specify the Customer on the Account Receivable line:

When you return to the original Credit Memo, you will see this at the top:

At the bottom you then assign the amount to the Credit Memo Invoice to close it ("pay" it):

The Partner Ledger will then show:

Note: the dates here are both 10/20 but in your case they would be the actual dates of the Credit Memo and Journal Entry based on when you posted them.