If you just wish to reverse the numbering - not the order - then you can use the following approach:

\documentclass{moderncv}
\usepackage{biblatex,refcount}
\makeatletter
% https://tex.stackexchange.com/q/66829/5764
\newcounter{numbibentries}
\renewbibmacro*{finentry}{\stepcounter{numbibentries}\finentry}
% https://tex.stackexchange.com/q/123805/5764
\defbibenvironment{bibliography}
{\list
{\printtext[labelnumberwidth]{% label format from numeric.bbx
\printfield{prefixnumber}%
\number\numexpr\getrefnumber{num-bib-entries}-\abx@field@labelnumber+1\relax}}
{\setlength{\topsep}{0pt}% layout parameters from moderncvstyleclassic.sty
\setlength{\labelwidth}{\hintscolumnwidth}%
\setlength{\labelsep}{\separatorcolumnwidth}%
\leftmargin\labelwidth%
\advance\leftmargin\labelsep}%
\sloppy\clubpenalty4000\widowpenalty4000}
{\endlist}
{\item}
\AtEndDocument{% Add reference at end of document to remember number of bib-entries.
\edef\@currentlabel{\thenumbibentries}\label{num-bib-entries}}
\makeatother
\moderncvstyle{classic}
\moderncvcolor{blue}
\firstname{John}
\familyname{Doe}
\addbibresource{biblatex-examples.bib}
\begin{document}
\makecvtitle
\nocite{companion,knuth:ct:a,knuth:ct:b}
\printbibliography[title={Publications}]
\end{document}
The idea is to count the number of references by tapping into each "\bibitem". Once all is counted, we insert a \label at the end of the document (using \AtEndDocument). This label is retrieved and used in a calculation (thanks to the expandable \getrefnumber from refcount) to reverse the numbering.
For multiple bibliographies per document, you could use \citesinthissection{<num>} as defined below:
\documentclass{moderncv}
\usepackage[defernumbers=true]{biblatex}
\makeatletter
\newcommand{\citesinthissection}[1]{\xdef\@totalcites{#1}}
% https://tex.stackexchange.com/q/123805/5764
\defbibenvironment{bibliography}
{\list
{\printtext[labelnumberwidth]{% label format from numeric.bbx
\printfield{prefixnumber}%
\number\numexpr\@totalcites-\abx@field@labelnumber+1\relax}}
{\setlength{\topsep}{0pt}% layout parameters from moderncvstyleclassic.sty
\setlength{\labelwidth}{\hintscolumnwidth}%
\setlength{\labelsep}{\separatorcolumnwidth}%
\leftmargin\labelwidth%
\advance\leftmargin\labelsep}%
\sloppy\clubpenalty4000\widowpenalty4000}
{\endlist}
{\item}
\makeatother
\moderncvstyle{classic}
\moderncvcolor{blue}
\firstname{John}
\familyname{Doe}
\addbibresource{biblatex-examples.bib}
\begin{document}
\makecvtitle
\nocite{companion,knuth:ct:a,knuth:ct:b}
\citesinthissection{3}% There are 3 cites in this section
\printbibliography[notkeyword=primary,title={Publications}]
\nocite{aristotle:anima,aristotle:physics}
\citesinthissection{2}% There are 2 cites in this section
\printbibliography[keyword=primary,resetnumbers=true,title={Other Publications}]
\end{document}
Remember to update the count of items whenever you add elements to your bibliography. Use the defernumbers=true global option and resetnumbers=true option from the second \printbibliography onwards. You may need to use options like keyword/notkeyword options in order to print exactly only what you want in each bibliography part.
\printbibliographywith something like\citesinthissection. That is,\citesinthissection{4} \printbibliography[..]...\citesinthissection{7} \printbibliography[..]... – Werner Mar 26 '15 at 18:20\citesinthissectionsuggestion. – Werner Apr 02 '15 at 04:53