In the novel The Mirror Crack'd from Side to Side, the Grices live on a Lower Farm. The farm is probably a large one or quite important because, for whatever reason, it gave the Grices the status as among those of a select few guests to be invited upstairs at Gossington Hall to meet Marina Gregg during the village fete.
There are two Lower Farms in the Miss Marple universe, both near St. Mary Mead and they may or may not be the same place.