Alex,
There is no hardware reset to the RTC module. After a SWRESET, the Scratch registers should be cleared.
There is a Wiki article about using the sleep mode. Have you looked at it and the example code that comes with it? I have to admit I have not looked at the code, but I found the article and expect it should be helpful to you.
You can search the TI Wiki Pages for "c6748 rtc" (no quotes) to find this article. Please let me know if you have trouble finding it.
Regards,
RandyP