So it turns out the problem was that Apache didn't have write permissions to the WEBROOT/var directory, so Magento was using its cache from the system /tmp directory. (thanks for the tip, Fiasco Labs!)

In case someone gets here from Google, I'll reiterate the steps...

How to Manually Change Domain in Magento

1. Update your core_config_data table to edit the two records for web/unsecure/base_url and web/secure/base_url

2. Delete the contents of WEBROOT/var/cache

3. Update / edit any .htaccess domain redirects you may have added

4. Restart Apache

5. Make sure Apache has write permissions to WEBROOT/var

6. If you created a new DB, ensure that the WEBROOT/app/etc/local.xml is pointing to it.

7. If you're using Chrome, clear your browser cache! (Chrome caches 301s)

    

   结合上述办法，数据库里这样做：

UPDATE `magento_dev`.`core_config_data` SET `value` = 'http://dd.local/' WHERE `core_config_data`.`path` = 'web/secure/base_url';UPDATE `magento_dev`.`core_config_data` SET `value` = 'http://dd.local/' WHERE `core_config_data`.`path` = 'web/unsecure/base_url';