Yes, I mean that SIQ writes look like any other write to the filesystem.  SIQ hands off the write to the filesystem layer just like any other protocol.  This will mostly affect the L2 cache on the target but should have less of an effect on L3 from a data caching perspective unless you do random reads from those data blocks while they are in L2 in which case putting those blocks in L3 is probably a good idea anyway.
I believe it's all in the title!  My setup is X410s + 2SSDs per node + L3 Cache enabled.  My understanding is NFS writes will be cached no matter what because they are buffered/coalesced, and later pushed to L3. This way the next read will avoid to hit the spinning disks.  But then, would a write from a SyncIQ policy run also end up in the cache? My gut feeling is it wouldn't.  The distinction here is quite important for our use pattern (occasionally reading from a SyncIQ replica).  Cheers,
Do SyncIQ writes end up in a caching layer?