def invalidate_dogpile_cache(cache_instance, hard=True):
    """
    The default invalidation system works by setting
    a current timestamp (using ``time.time()``)
    representing the "minimum creation time" for
    a value.  Any retrieved value whose creation
    time is prior to this timestamp
    is considered to be stale.  It does not
    affect the data in the cache in any way, and is
    **local to this instance of :class:`.CacheRegion`.**

    .. warning::

        The :meth:`.CacheRegion.invalidate` method's default mode of
        operation is to set a timestamp **local to this CacheRegion
        in this Python process only**.   It does not impact other Python
        processes or regions as the timestamp is **only stored locally in
        memory**.  To implement invalidation where the
        timestamp is stored in the cache or similar so that all Python
        processes can be affected by an invalidation timestamp, implement a
        custom :class:`.RegionInvalidationStrategy`.

    The method supports both "hard" and "soft" invalidation
    options.  With "hard" invalidation,
    :meth:`.CacheRegion.get_or_create` will force an immediate
    regeneration of the value which all getters will wait for.
    With "soft" invalidation, subsequent getters will return the
    "old" value until the new one is available.
    """
    cache_instance.invalidate(hard=hard)
