Example block caching

Problem/Motivation

It's a minor code issue in the example submodule, but it worth being noted.

Steps to reproduce

1. Enable the module and an Example Block submodule.
2. Add the block in the block structure.
3. Update currencies.
4. See that the block's output did not change.
5. Clear caches.
6. Block output updated.

Proposed resolution

Implement clearing of the block cache after currency updates to provide accurate and up-to-date conversions.