Drupal 7: Making Drupal block is no-cachable:

Drupal system makes blocks is cachable to speed render. The block cache is stored in Drupal core database block_cache table. By altering or change information of block as non-cachable. This is achieved by passing cache as "DRUPAL_NO_CACHE" in hook_block_info() for custom block and hook_block_info_alter() in existing block.