The local cache can be edited, as detailed in the official documentation located here in Semarchy xDM Plug-in Reference Guide.  

One frequent use-case for editing the Semarchy Email Enricher Domain Name Cache is to specify the domain name value that will be returned for records submitted with a specific value. This allows the Semarchy application to validate email domains against a local cache, vs doing an online lookup for this value. 

To edit the Semarchy Email Enricher Domain Name Cache, locate the EXTEMAILDOMAINS table. Look for the current domain name value in the HOST_NAME column. Change the SUGGESTION value to match your preferred return. 

One additional measure would be to change the HIT_COUNT value to a high number, since priority is given within the cache to SUGGESTIONS with higher HIT_COUNTS.