Is it okay to scan a book (that I own) strictly for personal use?
I am not a lawyer. This is a general caveat, and it is also why I don't know which copyright law applies: Australia's (where the book was published) or Germany's (where you reside). I would think Australia's, but I don't know for sure.

Under the laws of both countries it is illegal to make a full copy of a copyrighted book, but different exceptions apply. In brief: Under German and Austrian law, only manual copying is allowed. Under Australian law, you can legally scan a book that you own for your private use.

In Germany and Austria

According to the Urhebergesetz (copyright-holder law), a full copy may only be made by handwriting or -typing (§ 53 Abs. 4 Nr. 2 in Germany and § 42 (8) in Austria). This restriction also covers non-commercial personal and research purposes. An exception applies to works that have been out of print (for at least two years in Germany).

In Australia

The Copyright Act governs the reproduction of artistic, literary, dramatic, and musical works. Presumably this is an open list that includes also scientific works. The following information is taken from the official brochure "A Short Guide to Copyright Law".

In general, reproducing a copyrighted book is illegal, but there are exceptions.

There is a "fair dealing" exception for, inter alia, research purposes. Whether this exception applies depends on "the amount and substantiality of the portion copied". As a rule, several articles from a journal or one chapter from a book may be copied.

The most important exception for your case, however, is the format-shifting exception. It "allows certain types of material that a person owns to be copied into a different format for private or domestic use. For example, a book can be scanned into an electronic form".

Finally

On a pragmatic and ethical note: You bought the book, and there seems to be no ebook version that you could buy instead of scanning the book. Thus no harm is done if you scan it. As the German adage goes, "wo kein Kläger da kein Richter" (no plaintiff -- no judge).