I'm presently modifying a framework that was launched towards the public domain. Could it be ok that i can then to produce new framework according to some code in the public domain sourcetree as licensed under Apache ?

Wikipedia's meaning of Public Domain is:

The general public domain is a variety of abstract materials—commonly known to as intellectual property—which aren't possessed or controlled by anybody. The word signifies these materials are thus "public property", and readily available for anybody for any purpose.

So essentially, that you can do anything you want towards the code and release it under whatever license. However, the content also states:

Because proprietary privileges are founded in national laws and regulations, a product might be public domain in a single jurisdiction although not another.

Safe, I recommend getting in touch with the designers on this matter.

EDIT: As Jonathan Leffler stated inside a comment, the 2nd quote does not really apply within this situation. Different areas can define whenever a formerly copyrighted work makes its way into the general public domain, consider the code is particularly launched in to the public domain through the designers, it remains available to everybody, no matter their jurisdiction.