Hard drives are often used to store sensitive information. To protect this information from unauthorized disclosure, sanitize hard drives prior to reusing, decommissioning, or disposing of them.
Refer to your data protection policies to determine the most appropriate method to sanitize hard drives.
If required, take advantage of Oracle's Customer Data and Device Retention Service.
http://www.oracle.com/us/support/library/data-retention-ds-405152.pdf