Reset-O TCP flag means that the Reset is from the Outside.
Here is the syslog messages reference:
http://www.cisco.com/en/US/docs/security/fwsm/fwsm40/system/message/logmsgs_external_docbase_0900e4b18059d73b_4container_external_docbase_0900e4b180ef4f45.html#wp1280675
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