Hello!
It looks to me like you might be looking for something like the function call in DataPointEditDwr.java @ line 131. That file can be found https://github.com/infiniteautomation/ma-core-public/blob/21b40809b07fac6c74aa3905a6124e880ea2073b/Core/src/com/serotonin/m2m2/web/dwr/DataPointEditDwr.java for the source code.
The call that may help is,
Common.runtimeManager.purgeDataPointValues(point.getId());
Hope that helps! The alternative is probably to call DataPointEditDwr, and purge it through the tools already available. I have not tested these, yet, though, so let us know if it worked and how!