After some additional trials, I have just discovered that Workflow cache doesn't work exactly as I expected.
My goal was to retrieve details from a Youtube video and store them in Workflow cache. As I would repeat my workflow several times, it would make the most sense to have them cached to prevent other queries to the API.
As an example, I would type in Alfred: yd ckN-uJn9hAI (This will get details from the video at http://youtu.be/ckN-uJn9hAI). I would load each of the details I use more often in Workflow args and send those back to Alfred. I would select one, press