CP-6 Alternate storage site
What the standard requires
a. Establish an alternate storage site, including necessary agreements to permit the storage and retrieval of system backup information; and b. Ensure that the alternate storage site provides controls equivalent to that of the primary site.
Quoted verbatim from NIST SP 800-53 Rev 5 (OSCAL catalog), which is in the public domain.
Cross-framework mappings
No cross-framework mapping is seeded for this control. That is stated rather than filled in: a mapping nobody authored is worse than a gap you can see.
Track CP-6 with evidence behind it
In CMDash this control is a row with an owner, a status, uploaded evidence kept with its full history, and an export an assessor can read.