[Resource Timing] Definition of "network layer cache"

The Resource Timing spec says:

"Resources that are retrieved from the user agent's networking layer cache
must be included as PerformanceResourceTiming objects in the Performance
Timeline."

What exactly constitutes a "networking layer cache?" Blink's memory cache
seems to behave differently than IE10's. When navigating pages on the same
site, Blink uses the "in-memory cache" and reuses subresources without
fetching. That means we don't report Resource Timing for these resources.
IE10 seems to always report resources in the same circumstances.

To try it out, visit webpagetest.org. Note the "site.js loaded in x
milliseconds" at the bottom of the page. Browse to the "About" page on
webpagetest.org. That message disappears on Chrome, it shows a new value on
IE10.

Are we both compliant in our own ways? Or do we need to better define
"network layer cache?"

James