Since INMEMORY allows the INEMOMERY and its compression settings to be at the column level, when looking at what we have INMEMORY, besides v$im_segments, we need to also look at V_$IM_COLUMN_LEVEL.
When checking for INMEMORY, I look at:
dba_tables – Is the table configured for INMEMORY.
v$im_segments – Has the table actually been loaded into INMEMORY, and if so, is it completely loaded so it can be used?
v_$im_column_level – Which of the columns are INMEMORY?