Comment 231 for bug 445852

@Trey
Have you tried using the ATA 'Secure Erase' command (see: https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase). This tells the disk drive's controller to do the resetting, allowing data that dd cannot reach to be reset. Also as a by product it will reset the SSD's speed back to the performance you had on day one (see the link above for more info).
hope this works.