Rebuilding a day's stats?

I have a peculiar problem. Piwik normally mostly-works on my DreamHost installation of it (I'll be moving it later, but until then..), but we got hit pretty hard the last few days.

Specifically, it was bad enough that this happened:

(To be specific, the day with 0 is wrong; it was at least 30,000 before it turned into 0. The next day is just leftovers from the initial spike and is normal.)

Is there any way to rebuild the stats for a specific day, or is the only way to rebuild everything?

As per the FAQ How do I force the reports to be re-processed from the logs? there are several methods.

You can drop the tables piwik_archive_blob_YYYY_MM and piwik_archive_numeric_YYYY_MM containing the date you want to be rearchived. This is the method I had used.

Alternatively you can temporarily add:

[Debug]
always_archive_data_day = 1 

to your config/config.ini.php to force archiving of daily reports.