Method and apparatus for managing a front-end cache formed of ferroelectric memory element (FME) cells. Prior to storage of writeback data associated with a pending write command from a client device, an intelligent cache manager circuit forwards a first status value indicative that sufficient capacity is available in the front-end cache for the writeback data. Non-requested speculative readback data previously transferred to the front-end cache from the main NVM memory store may be jettisoned to accommodate the writeback data. A second status value may be supplied to the client device if insufficient capacity is available to store the writeback data in the front-end cache, and a different, non-FME based cache may be used in such case. Mode select inputs can be supplied by the client device specify a particular quality of service level for the front-end cache, enabling selection of suitable writeback and speculative readback data processing strategies.