This is what `shred` and other secure wipes do. There is some concern over data stored in sections which the firmware has swapped out and made inaccessible. But

This is what `shred` and other secure wipes do. There is some concern over data stored in sections which the firmware has swapped out and made inaccessible. But if this is a concern to you, then you should be using full disk encryption anyway which makes all of this a non issue.