Well I'm not 100% clear on the terminology, but there are two caches, both configured through the Intel RST app, which lose their settings each reboot.
One is under "manage array" and is called "disk data cache". It has two settings, enabled and disabled. I set it to enabled but it resets to disabled each time I reboot.
The other is under "manage volume -> advanced" and is labelled "cache mode" - you can select write-back, write-through, read only or off. It is returning to "off" after I set it as "write back".
Hope that clarifies 