ADS and SGS both store the customer domain, but to different tables.

ADS stores the domain to the mms_common.accounts table

SGS stores the domain to the site_generation.hostingAssignments table

SGS should probably control this setting. SGS domain changes should probably be audited - may indicate a mismatch with ADS. ADS should probably validate against the SGS value and fail or at least audit mismatches. Not clear why ADS is saving it currently.