When caching a workflow, editing a tool should only remove the cache as of the edited tool

[kklc]

I often have to cache my workflow at certain points to do further development/analysis since the run time is so long. I can't express how frustrating it is when i need to edit a formula tool that's like 2 tools behind the cache but the whole entire cache is lost when i have to edit it. why can't the cache be kept up until the tool that was edited??