Hi Rama,
Have you have seen Adobe Security guidelines?
http://wwwimages.adobe.com/content/dam/acom/en/marketing-cloud/campaign/pdfs/54658.en.campaign.wp.adb-security.pdf
If your instance is hosted by Adobe, ask support to install GPG utility on the server.
Get public-private key pair generated for outbound transfer.
While doing export, you can encrypt the file on Campaign server and also provide the public key to external sFTP server team for decrypting the file. And use vice-versa to decrypt the file to decrypt at adobe campaign.
This can be done in file load activity and js activity, and for all the transfer via the database, it happens via secure transfer so that should be covered.
For deletion, if it's hosted by Adobe you are covered because it's Adobe's responsibility to ensure the compliance if it's on the premise, Move all the data marked as delete to an Archiving location and use Gutmann method to delete which will ensure that you are covered.
https://en.wikipedia.org/wiki/Gutmann_method
A sample tool buit ontop of this method, use this for Linux environments.
http://manpages.ubuntu.com/manpages/xenial/en/man1/shred.1.html
PS: Build a new strategy for data sharing between two markets based on the permission.
Regards,
Amit