/-------\
| Start |
\-------/
    |
    |
    v
----------------------------------------------------
| (1) Obtain the digest of content to be validated |
----------------------------------------------------
    |
    |
    v
   / \
  /   \
 /     \       /------\
/  (2)  \----->| Stop |
\  "a"  /  Y   \------/
 \     /
  \   / 
   \ /
    |           "a" == Does any copy of content already in the cache
    | N                possess a digest matching that of the content
    |                  to be cached?
    v
 -------        "b" == Obtain a copy of the content to be validated
 |     |               and store it in the cache.
 | (3) |
 | "b" |
 |     |
 -------
    |
    |
    v
/-------\
| Stop  |
\-------/