Hello,   This is not the cache itself.  There's nothing to "flush"  This is the battery that backs up the cache on the controllers in case of a power failure.  There is no command to fix this.   Don   
Hi everybody! I have the storage with Warning of "end of life" the controllers and the event is "The service life of the control module cache battery is 90 percent depleted". The hardware is out of warranty, something can be done to fix without disabling the Warning notification   Thanks Regards    
Equallogic PS610E Battery end of life Warning- 90 Percent cache