Caching is one of the most common techniques used to make applications faster. Instead of fetching the same data from a database or API every time a user requests it, an application can temporarily store that data in a cache. The next request can then be served much faster. But this raises an important question: If the original data changes, how does the cache know that its copy is no longer correct? The short answer is: a cache usually does not magically know. The applicatio