dnf caches

[Pádraig Brady]

My Fedora 22 system prompted me that there was a new coreutils package for update.
Rather than clicking "restart and install" in the GUI I tried to:

  # dnf install coreutils
  Using metadata from Tue Apr 21 19:54:02 2015 (1 day, 21:50:24 hours old)
  Package coreutils-8.23-8.fc22.x86_64 is already installed, skipping.

Ok fair enough, the updating system is using a separate cache to dnf.
Not ideal, but anyway how do I update the dnf cache?
I tried:

  # dnf check-update coreutils
  Using metadata from Thu Apr 23 17:42:54 2015 (0:01:19 hours old)
  coreutils.x86_64

Given the above found the new coreutils, I thought an install
would now work, though unfortunately it doesn't.

Shouldn't dnf be looking at the timestamps of the repo
in each invocation (without -C) and updating the metadata if needed?
I presume that's what yum does since I never had an issue with this.

I tried explicitly cleaning the cache like this:

  # dnf --disablerepo=* --enablerepo=updates clean metadata
  Cleaning repos: updates
  5 metadata files removed
  2 dbcache files removed

How do I refresh the cache?
Why should I need to mess with it anyway?

thanks,
Pádraig.

p.s. If using yum legacy, does that in fact use another (3rd) cache?